I installed a new dryer in our house. It runs but won't heat. It has a 240V 3 wire connection. There is a 30 amp double pole breaker installed in the breaker box. (the box is very old) I've read that you should get 120V from each leg to the neutral which I do. I also read that you should get 240V across the two. Only a few volts register on the meter, not 240. How is this possible and what changes should I make to correct this?
You have one of these.
It's not a 2-pole breaker. It's a twin, duplex, tandem, cheater or double-stuff breaker giving two 120V circuits in a single space in the panel, intended to be used for 120V circuits when you have run out of space in the panel. That doesn't work as discussed here. One space can only access 120V.
You need a 2-pole breaker.
If you have run out of space in the panel, they make 240V 2-pole double-stuffs; they take 2 spaces, contain 4 breakers, with the middle two tied together providing your 240V circuit. They are available with or without the outer tie. These are not simply handle-tied; there is also an internal mechanism doing the tying. Hence you cannot simply add ties to 120V breakers, unless the manufacturer says you can.
Look at the vertical location of your double pole breaker. The first 2 slots in a column are on one phase, the next two are on the other phase. A double pole breaker has to have one connection to each phase, so it has to start on an even location. Look at the breaker for the stove, your dryer needs to be an even number of locations away from it.